1. Field of the Invention
The present invention relates to a method of fabricating a flash memory and an isolating structure applied to a flash memory, and more particularly, to a method and a structure that improves the process window during floating gate fabrication.
2. Description of the Prior Art
A flash memory is a non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards or USB flash drives, which are used for general storage and transfer of data between processors and other digital products. Scaling down of flash memory cells is considered critical to continue the trend towards high device density.
Generally speaking, the basic flash cell consists of a floating gate, a dielectric layer and a control gate stacked on a tunnel oxide layer from bottom to top in sequence. The floating gate is for charge storage, and the control gate is for controlling the charging/discharging of the floating gate. In order to increase the performance of flash, a floating gate wing is formed at two sides of the floating gate. In this way, a gate coupling ratio (GCR) is increased. The higher the GCR, the shorter the programming and erasing time that can be reached. The operation efficiency is therefore increased.
However, in 90 nm manufacturing processes, the alignment accuracy tolerance of floating gate wing fabrication must be controlled below 30 nm, which is a great challenge for conventional methods.